Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
2002-05-09
2003-11-04
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S725000, C343S895000, C343S867000
Reexamination Certificate
active
06642893
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-band antenna system including a retractable whip antenna and a meander antenna having a plurality of selectively coupled meander radiating elements formed on a dielectric flexible board. The meander antenna may include one or more passive elements which may be selectively coupled to the meander radiating elements of the meander antenna.
2. Description of the Related Art and the Relationship of the Instant Invention Thereto
In the rapidly evolving technology of cellular communication, there is an emerging thrust on the design of multi-purpose cellular handsets. A cellular handset which has system capabilities of both dual cellular and non-cellular (such as GPS) applications has become a new feature. Thus, there is a growing trend to design antennas which operate in both the dual cellular and non-cellular frequency bands. The inherent problem facing such a design is the bandwidth requirement at the upper resonance of the antenna to simultaneously cover both the GPS band (1575 MHz) and the upper cellular band such as either DCS (1710-1880 MHz) or PCS (1850-1990 MHz). The combined bandwidth requirement to cover the GPS and PCS bands of operation approximates about 23.35%. The easy recourse of an additional antenna with a separate feed to cover the GPS band alone has not proved to be an attractive alternative. In view of this, a single feed multi-band antenna operating both in the dual cellular and non-cellular bands is a topic of considerable importance for cellular applications. The instant invention is a new method of designing a single feed multi-band retractable antenna operating in the dual cellular bands (AMPS/PCS) as well as non-cellular (GPS) band. The significant aspect of this invention pertains to the design of the single feed, multi-element meander antenna as the primary radiator in the retracted position of a multi-band whip antenna. In this invention, a multi-element meander antenna or radiator replaces the conventional helical coil radiator to constitute the primary radiator for the retracted position of a multi-band whip antenna.
A conventional prior art multi-band retractable antenna
100
for a cellular handset
101
is shown in
FIGS. 16A and 16B
.
FIG. 16A
illustrates the multi-band retractable antenna in its retracted position. A plastic housing or sheath
102
fully encloses a helical coil radiator or a meander radiator positioned therein. The plastic housing
102
is usually mounted near one of the corners at the top edge
103
of the handset
101
. The plastic housing
102
with a helical coil radiator or meander radiator therein is usually positioned so as to have an outward extension with respect to the top edge
103
of the handset
101
. Such a position is conducive for good antenna radiation characteristics. In the retracted position of the multi-band retractable antenna,
100
, as depicted in
FIG. 16A
, the whip antenna
104
with stopper
105
mounted thereon is decoupled from the helical coil radiator or meander radiator positioned within the plastic housing
102
. Only the radiator inside the plastic housing
102
is allowed to retain contact with the RF connector
106
placed on the chassis
107
of the handset
101
. In the retracted position of the multi-band antenna
100
, the helical coil radiator or meander radiator alone is the dominant or primary radiator with an insignificant contribution of the whip antenna
104
.
FIG. 16B
illustrates the configuration of the prior art multi-band antenna
100
in its extended position. In this configuration, the whip antenna
104
is pulled up and through the connector
106
with the stopper
105
of the whip antenna
104
making contact with the RF connector
106
. In the extended position, along with the whip antenna
104
, the helical coil radiator or meander radiator positioned within the plastic housing
102
is also connected to the RF connector
106
. When the whip antenna
104
is in the extended position, the dominant radiator of the retractable multi-band antenna
100
, however, is the linear whip antenna
104
with its length designed at least for the quarter wavelength of operation and extending well above the plastic housing
102
. It is of importance to note that the coupling between the whip antenna
104
and the helical coil radiator or meander radiator requires optimization to obtain the desired radiation characteristics of the whip antenna.
In most conventional multi-band retractable antenna designs, the dominant or primary radiator in the retracted mode is usually an ordinary helical coil. With a single coil of simple geometry, realizing a multi-band operation with satisfactory bandwidth imposes the requirement of an external matching network. If the desired frequency bands of operation include more than two bands, e.g. AMPS/GPS/PCS or GSM/GPS/DCS, the design of the helical coil is an involved task. Such a multi-band retractable antenna design may result in a complicated helical coil which is difficult to fabricate. Therefore, the design of a multi-band radiating element which is easy to fabricate is desirable. In the proposed invention, resorting to the meander radiator planar technology, a radiator in the form of a plurality of meander radiating elements is designed and etched on a dielectric flexible board resulting in fabrication ease. Unlike the design of a conventional helical coil, the design of the meander radiator on the flexible board does not impose any constraint on the complexity of the antenna structure from a fabrication point of view. Any arbitrary variations in the profiles of the radiating elements of the meander radiator on the flexible board can be easily and consistently reproduced with relative ease. This is a distinct advantage of the choice of the meander radiator over conventional helical coils as the primary radiator in the retracted position of multi-band retractable antennas.
In the design of a retractable antenna, the input impedance of the whip (wire) antenna (normally of quarter wavelength or more in its length) is different from the desirable 50 ohms. The deviation of the input impedance from the desired nominal impedance of 50 ohms depends mainly on the chosen length for the whip antenna as well as the chassis or associated ground plane of the radio device. To realize the impedance match at the RF input port of the radio or communication device, an external matching circuit with discrete inductors and capacitors is common in most of the prior art designs. Apart from the external matching network for the extended position, a separate and additional external matching network for the impedance match for the radiator in the retracted position may also be needed. Such a necessity arises to obtain the impedance match of the helical coils (which are the dominant radiators in the retracted mode) at the RF input port of the device. Therefore alternate designs of multi-band retractable antennas devoid of either the single or dual external matching networks are of significant importance for cellular communication. This invention proposes the design of multi-band retractable antennas without necessitating the requirements of impedance matching networks either for the extended or the retracted positions. In this invention, the meander radiator is designed for a self-impedance match in the retracted position. In addition, the meander radiator is also designed to serve the analogous role of an external matching network to realize the impedance match for the whip antenna in the extended position of the multi-band retractable antenna. The proposed invention circumvents the necessity of an external matching network to realize the design of a single feed multi-band retractable antenna whose upper resonant band itself comprises multiple frequency bands with wider separation between them such as GPS/PCS bands.
In the recent past, there is an emerging trend for a closer look at the impedance characteristics of antennas toward optimizing gain performance thereof. The current con
Hardy Willis R.
Hebron Ted
Kadambi Govind R.
Song Ying Dong
Centurion Wireless Technologies, Inc.
Holland & Hart
Phan Tho
LandOfFree
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